Oscillatory shear polymer melts

To date, the melt state linear dynamic oscillatory shear properties of various kinds of nanocomposites have been examined for a wide range of polymer matrices including Nylon 6 with various matrix molecular weights [34], polystyrene (PS) [35], PS-polyisoprene (PI) block copolymers [36,37], poly(e-caprolactone) (PCL) [38], PLA [39,40], PBS [30,41], and so on [42],... 

Mills,N.J., Nevin,A. Oscillatory shear measurements on polystyrene melts in the terminal region. J. Polymer Sci. Pt. A-2 9,267-281 (1971). 

Consider tor example, a melt of 1,4-poly butadiene linear chains with M—130000gmol The molar mass of a polybutadiene Kuhn monomer is Mo= I05gmol (see Table 2.1) so this chain has N = MjMo 1240 Kuhn monomers. At 25 °C, this polymer is 124 K above its glass transition and its oscillatory shear master curve is shown in Fig. 9.3. The time scale for monomer motion is tq = 0.3 ns, An entanglement strand of 1,4-polybutadiene has molar mass M — I900gmol (see Table 9.1) and therefore contains N — M jMQ= % Kuhn monomers. The whole chain has N/Ne = MjMs 68 entanglements. The Rouse time of the entanglement strand Te = 0.1 ps [Eq. (9,16)]. 

Jeyaseelan and Giacomin (1995) examine the use of large-amplitude oscillatory-shear (LAOS) rheology of filled polymer melts (HDPE filled with carbon black) and use transient-network theory (which separates filler and polymer entanglement effects) to describe the non-linear flow behaviour. 

Various instruments are available to measure the viscosity of polymer melts and solutions, and more generally their rheological behavior, which include capillary and rotational viscometers. The former can be used to measure parameters such as shear viscosity, melt fracture, and extensional viscosity, which are important for many polymer processes. The latter type of device can be used in either steady or oscillatory mode, thus providing a measure of the viscosity as well as viscoelasticity (G", G, and tan 5) as a function of frequency and temperature. 

Mutel, A.T. Kamal, M.R. (1986). Characterization of the Rheological Behavior of Fiber-Filled Polypropylene Melts under Steady and Oscillatory Shear using Cone-and-Plate and Rotational Parallel Plate Rheometry. Polymer Compwsites, Vol.7, No.5, pp. 283-294ISSN0272-8397... 

A number of experimental methods have been applied to measure the melt viscosity of polymers (53-55,65), but capillary extrusion techniques probably are generally preferred. Rotational methods are also used, and some permit the measurement of normal stress effects resulting from elasticity as well as of viscosity. Slit rheometers can also be used to measure normal stress (66). Oscillatory shear measurements are useful for measuring the elasticity of poljmier melts (57,58). Controlled stress methods have also been applied (59). Squeeze film flow has also been proposed as a geometry suitable for processibility testing of polymer melts... 

Mutel, A.T. and Kamal, M.R. (1986) Qiaracterization of the rheological behavior of fiber-filled pol3 ropylene melts imder steady and oscillatory shear using cone-and-plate and rotational parallel plate geometry, Polym. 

Although stress-relaxation and creep measurements are used extensively, measuring oscillatory shear is the most commonly used method for characterizing the linear viscoelastic properties of polymer melts and concentrated solutions. As indicated in Fig. 3.10, the liquid is strained sinusoidally at some frequency co, and in the linear region (small-enough strain amplitude yo)- The stress response at steady state is also sinusoidal, but usually out of phase with the strain by some phase angle steady-state stress signal is resolved into in-phase and out-of-phase components, and these are recorded as functions of frequency ... 

Oscillatory shear measurements can be done with the parallel-disk arrangement in a manner similar to the case of the cone-n-plate viscometer and, similarly, the material fimcdons i), G, C, and others can be generated. However, a slightly different tedinique [36] is at times used wherein the polymer melt sample is deformed between two oscillating parallel eccentric disks as shown in Fig. 3.2. In this case, too, it has been shown that the fluid elements undergo a periodic sinusoidal deformation and the forces exerted on the disk are thus interpreted in terms of G and G" [4]. 

Mutel, A. T. and Kamal, M. R., Characterization of the rheological behavior of fiber-filled polypropylene melts under steady and oscillatory shear using cone-and-plate and rotational parallel plate geometry, Polym. Compos., 1, 283-294 (1986). Sacks, M. D., Khadilkar, C, S., Scheiffele, G. W., Shenoy, A. V., Dow, J. H., and Sheu, R. S., Dispersion and rheology in ceramic processing, Adv. Ceram., 24, 495-515 (1987). 

---